Re: [pushed] [gdb/testsuite] Fix gdb.threads/dlopen-libpthread.exp for upstream glibc

[Simon Marchi <simark@simark.ca>]

On 12/30/22 10:54, Tom de Vries via Gdb-patches wrote:
> On ubuntu 22.04.1 x86_64, I run into:
> ...
> (gdb) info probes all rtld rtld_map_complete^M
> No probes matched.^M
> (gdb) XFAIL: gdb.threads/dlopen-libpthread.exp: info probes all rtld rtld_map_complete
> UNTESTED: gdb.threads/dlopen-libpthread.exp: no matching probes
> ...
> This has been filed as PR testsuite/17016.
> 
> The problem is that the name rtld_map_complete is used, which was only
> available in Fedora 17, and upstream the name map_complete was used.
> 
> In the email thread discussing a proposed patch (
> https://sourceware.org/legacy-ml/gdb-patches/2014-09/msg00712.html ) it was
> suggested to make the test-case handle both names.
> 
> So, handle both names: map_complete and rtld_map_complete.
> 
> This exposes the following FAIL:
> ...
> (gdb) info sharedlibrary^M
> From To    Syms Read Shared Object Library^M
> $hex $hex  Yes       /lib64/ld-linux-x86-64.so.2^M
> $hex $hex  Yes (*)   /lib/x86_64-linux-gnu/libgtk3-nocsd.so.0^M
> $hex $hex  Yes       /lib/x86_64-linux-gnu/libc.so.6^M
> $hex $hex  Yes       /lib/x86_64-linux-gnu/libdl.so.2^M
> $hex $hex  Yes       /lib/x86_64-linux-gnu/libpthread.so.0^M
> (*): Shared library is missing debugging information.^M
> (gdb) FAIL: gdb.threads/dlopen-libpthread.exp: libpthread.so not found
> ...
> due to using a glibc (v2.35) that has libpthread integrated into libc.

On my Ubuntu 22.04, I now get:


    info sharedlibrary^M
    From                To                  Syms Read   Shared Object Library^M
    0x00007ffff7fc5090  0x00007ffff7fee335  Yes (*)     /lib64/ld-linux-x86-64.so.2^M
    0x00007ffff7da7700  0x00007ffff7f39abd  Yes (*)     /lib/x86_64-linux-gnu/libc.so.6^M
    0x00007ffff7fb70a0  0x00007ffff7fb721f  Yes         /home/smarchi/build/binutils-gdb/gdb/testsuite/outputs/gdb.threads/dlopen-libpthread/dlopen-libpthread.so^M
    (*): Shared library is missing debugging information.^M
    (gdb) FAIL: gdb.threads/dlopen-libpthread.exp: libpthread.so found

And this is what I expect, given that libpthread.so doesn't exist
anymore.  I don't understand the output you pasted above.  My
testsuite/outputs/gdb.threads/dlopen-libpthread/dlopen-libpthread.so
doesn't depend on libpthread.so.0.  I think that libpthread.so.0 is just
there fore backwards compatibility with old binaries that refer to it,
but any newly compiled binary will not depend on it.  So the binary
compiled by the test should not.  I also don't understand where the
libgtk3-noscd.so.0 library comes from, it's a bit strange to have that
in a test binary.

> 
> Fix this by changing the FAIL into UNSUPPORTED.
> 
> Tested on x86_64-linux.
> 
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=17016
> ---
>  .../gdb.threads/dlopen-libpthread.exp         | 35 +++++++++++++------
>  1 file changed, 25 insertions(+), 10 deletions(-)
> 
> diff --git a/gdb/testsuite/gdb.threads/dlopen-libpthread.exp b/gdb/testsuite/gdb.threads/dlopen-libpthread.exp
> index 5c3d8a34c30..dcc48260e88 100644
> --- a/gdb/testsuite/gdb.threads/dlopen-libpthread.exp
> +++ b/gdb/testsuite/gdb.threads/dlopen-libpthread.exp
> @@ -40,22 +40,37 @@ if { ![runto_main] } {
>      return -1
>  }
>  
> -set test "info probes all rtld rtld_map_complete"
> -gdb_test_multiple $test $test {
> -    -re "\[ \t\]rtld_map_complete\[ \t\]+0x\[0-9a-f\]+.*\r\n$gdb_prompt $" {
> -	pass $test
> -    }
> -    -re "No probes matched\\.\r\n$gdb_prompt $" {
> -	xfail $test
> -	untested "no matching probes"
> -	return
> +set probe_names {}
> +# Fedora 17 name.  There's specific code in
> +# svr4_find_and_create_probe_breakpoints to deal with this.
> +lappend probe_names rtld_map_complete
> +# Upstream name.
> +lappend probe_names map_complete
> +
> +set have_probe 0
> +foreach probe_name $probe_names {
> +    set cmd "info probes all rtld ^$probe_name$"
> +    gdb_test_multiple $cmd "" {
> +	-re -wrap "\[ \t\]$probe_name\[ \t\]+0x\[0-9a-f\]+.*" {
> +	    set have_probe 1
> +	}
> +	-re -wrap "No probes matched\\." {
> +	}
>      }
>  }
>  
> +if { !$have_probe } {
> +    untested "no matching probes"
> +}

I think you are missing a "return" here, to match the previous behavior?

> +
>  set test "libpthread.so not found"
>  gdb_test_multiple "info sharedlibrary" $test {
>      -re "/libpthread\\.so.*\r\n$gdb_prompt $" {
> -	fail $test
> +	# With newer glibc, libpthread has been integrated into glibc so we
> +	# can expect it to be already loaded at main.  This means we no longer
> +	# excercise the scenario we're trying to trigger, but continue
> +	# nevertheless.
> +	unsupported $test

Given this comment here, it looks like your something in your
environment makes it so libpthread.so.0 is loaded at startup, but I
don't think it's supposed to happen in a "clean" state.  Indeed,
libpthread has been merged into libc, but that doesn't mean that any
program will show libpthread.so.0 as loaded.  There must be something
strange happening here.  Did you have some LD_PRELOAD set or something?

Simon